The overall proposal involves characterization of the uterine receptor for oxytocin, thestudy of the biochemical changes resulting from oxytocin-receptor interaction, and investigation of factors which regulate these changes. For the next year we will examine: 1. The effect of oxytocin antagonists on the binding of (H3 oxytocin to rat uterus. 2. The purification of subcellular fractions binding (H3) oxytocin from uterine homogenates by sucrose density gradient centrifugation. 3. The effect of estrogen on the affinity of the uterine receptor for oxytocin. 4. The binding ff (H3) oxytocin to receptors in the rat oviduct. 5. The binding of (H3) oxytocin to dispersed uterine myometrial cells. 6. The effect of oxytocin on adenylate cyclase in uterus and mammary tissue.